1. Field of the Invention
The present invention relates to an improved power semiconductor module having active and passive components including a power converter module. More specifically, the present invention relates to a power semiconductor module that includes a housed (encapsulated) power semiconductor element having contact elements and offers substantial manufacturing advantages.
2. Description of the Related Art
Several power semiconductor modules with active and passive components (including power converter modules) have been described in the literature. Unfortunately, efforts to improve performance capacity, reliability, and life expectancy, while simultaneously decreasing manufacturing costs have been unsuccessful
Modern power semiconductor modules, are modules without base plates, as can be seen in, for example DE 199 03 875 A1. This type of modern power semiconductor module includes:                (1) an outer housing,        (2) a ceramic substrate supporting circuit-capable metallic laminations arranged, for example, by the DCB (direct copper bonding) process,        (3) electronic components such as diodes, transistors, resistors or sensors applied with positive connections to the substrate by means of a soldering technique,        (4) bondings that join the structured side of an unhoused (unencapsulated) chip-shaped power semiconductor components with other components and/or the substrate and/or the connecting elements leading outside, and        (5) a rubber-bonding (preferably silicone based) compound surrounds each of the electronic components and electrically insulates the individual components.        
One disadvantage of the conventional design is that, particularly for large-surface solder joints on heat sinks, it is difficult to predictably control the quality of the solder joint. Low-quality solder joints and lack of process predictability reduce the reliability and the life expectancy of the resultant power semiconductor modules. Consequently, it has been found advantageous for power semiconductor modules to use a configuration that provides a pressure contact solely between the module and the heat and eliminates the need to solder the module directly to the heat sink.
Unfortunately, pressure buildup in pressure-contacted power semiconductor modules is conventionally accomplished by means of a mechanically stable pressure plate. Depending on the type of conventional embodiment, the produced pressure is transmitted directly to the substrate by specifically designed pressure pieces of the pressure plate, (as shown in DE 196 48 562 C1), or by an elastic pressure accumulator (as shown in DE 199 03 875 A1).
Unfortunately, the power semiconductor modules shown in DE 196 48 562 C1 and DE 199 03 875 A1, as is customary in modern modules, have the disadvantage of requiring a large and complex array of power semiconductor elements. Each of these power semiconductor elements must be reliably, cheaply, and quickly contacted either with each other, or with a substrate. Technically, these connections (alternatively known hereinafter as bondings or solderings) are accomplished by a large number of individual wire bondings (wire solderings), often positioned in awkward and tight configurations. These bondings extend from the middle/top portion of a power semiconductor element to an outer contact surface. Consequently, it is quite common to use up to ten (10) bondings per component to ensure reliability in a range of difficult environments. Since each of the bondings is necessarily made in a serial-production manner (one wire bonding at a time), their manufacture takes considerable time and thus represents a substantial portion of the manufacturing cost of each power semiconductor module. Efforts to speed up this serial manufacturing process, by employing quicker machine actuation, has reached a plateau in recent years. Additionally, since each bonding requires space in the module, the large number of bondings prevents simple module minimization.
Referring now to FIG. 1, a power semiconductor module on a heat sink 10 in a housing 60 includes, a substrate 20 with a first metallic lamination 210 contacting heat sink 10, and a second metallic lamination 220 (also known hereinafter as a contact element 220) opposite heat sink 10. Second metallic laminations 220 (contact elements 220) are formed in a conventional circuit-friendly structure (as required by the circuit design) and operate as electro-conductive contact surfaces.
Multiple unhoused (unencapsulated) chip-shaped power semiconductor elements 30 are arrayed on, and electrically connect with, second metallic laminations 220, as shown. Conventionally, bonding techniques used to join second metallic laminations 220 with power semiconductor elements 30 include forming a soldered joint or an adhesive bonded joint. This type of adhesive bonded joint is established with electrically conductive adhesives.
Additional electrical bondings, formed as wire bondings 310, are soldered to and extend from a top surface of power semiconductor elements 30 (opposite substrate 20) and contact and are soldered to second metallic laminations 220 (contact elements 220). Main connections 70 and auxiliary connections 80 are secured to substrate 20 to enable later electrical connection between the power semiconductor module and external components. Alternative components may include a sensor 50 and are secured to substrate 20 as desired by a manufacturer. Finally, after conventional assembly, the individual electrical components are electrically insulated by and covered with a sealing compound 90.
Unfortunately, the necessary use of sealing compound 90 with the conventional design eliminates non-destructive testing of components, easy replacement of components, and easy repair of the entire power semiconductor module.